1. Field of the Invention
This invention relates to a seek error retry method of disk device and its disk device to perform retry control when a seek error has occurred during head seeking, and in particular relates to a seek error retry method of disk device and its disk device, which is suitable for a disk device having a ramp mechanism to retract a head from the disk media.
2. Description of the Related Art
A disk device employing a magnetic disk, magneto-optical disk, optical disk, or other storage media performs a seek operation to position the head at a desired track on the disk. In such a disk device, as the head flying height is reduced, use of the CSS (Contact Start-Stop) method becomes difficult. Moreover, there are demands for disk devices with improved resistance to shocks when not in operation.
Consequently devices adopting a ramp-load method have been proposed. In a ramp-load method, a ramp mechanism is provided on the external perimeter of the disk, and while not in operation the head is retracted from the disk to the ramp mechanism. FIG. 9 shows the configuration of a magnetic disk device adopting a conventional ramp-load method.
As shown in FIG. 9, a magnetic disk 160 is provided on the spindle 120 of the magnetic disk device. The magnetic head 110 which reads information on the magnetic disk 160 moves in the radial direction of the magnetic disk 160. A ramp mechanism 111 is provided at the outermost perimeter of the magnetic disk 160. The ramp mechanism 111 has an inclined portion 111-1 and a depressed portion 111-2.
In a ramp-load method, when operation ends the magnetic head 110 is moved to the ramp mechanism 111, as indicated by the direction of the arrow UL. The magnetic head 110 rides over the inclined portion 111-1 of the ramp mechanism 111, and is accommodated in the depressed portion 111-2 (this is called an unload operation). On the other hand, when starting operation the magnetic head 110 is moved from the ramp mechanism 111 to the magnetic disk 160, as indicated by the direction of the arrow LO. The magnetic head 110 moves from the depressed portion 111-2 to the inclined portion 111-1 of the ramp mechanism 111 to return to the magnetic disk 160 (this is called a load operation). At the time of this load operation, for example the velocity is detected based on the back-electromotive force of the VCM (actuator) driving the magnetic head 110, and the velocity is controlled at a prescribed velocity to load the magnetic head 110 and prevent crashes.
In the prior art, when seeking in the outward direction, if a seek error occurs the magnetic head 110 is immediately stopped, and a current flows in the inward direction (current in the opposite direction), causing motion in the inward direction, to perform a seek error retry (see for example Japanese Patent Laid-open No. 2004-178790).
In recent years, the densities of magnetic disks 160 have risen and the area up to the outermost perimeter have been used as a data zone, in order to increase storage capacities; and in order not to detract from performance as capacities are increased, there has been a demand for faster seek velocities. For example, in sampled servo operation during seeking, the head moves over 200 to 300 tracks for one sample.
Hence in the prior art, when there is a degree of velocity outward during seek error detection, and when seek error detection is delayed, there is the danger that the head 110 may ride over the ramp mechanism 111. If current in the inward direction is begun in this state, due to high-speed loading action the head 110 may collide with the magnetic disk 160, causing a crash between the magnetic head 110 and magnetic disk 160.
In particular, when the disk storage density is high and the data zone is extended outward for increased storage capacity, if a seek error occurs during outward-direction seeking, the head may readily climb onto the ramp mechanism.